This program is designed to extend our understanding of the role played by alterations in bone blood flow (BF) in the pathology and physiology of bones and joints. Four areas of study are planned. 1) Osteonecrosis of the capital femoral epiphysis in congenital dislocation of the hip. Our experiments will be designed to demonstrate the changes in blood flow in the capital femoral epiphysis after cast immobilization and surgical reduction of the congenitally dislocated hip. This information will be used to determine the treatment regimens least dangerous to the epiphysis in infants and more mature animals. 2) Osteoarthrosis and bone flow. We plan to develop a reliable experimental model for osteoarthrosis, and follow the sequence of biochemical changes in the cartilate and subchondral bone. Our goal is to correlate these events with changes in subchondral bone blood flow. This will allow us to demonstrate the interrelationships of changes in the cartilage and subchondral bone more completely than has been possible before. 3) Acute hormonal effects on bone blood flow. The objective of these experiments will be to correlate the changes in bone blood flow with acute changes in serum ion concentrations elicited by normonal and ionic challenges. This study should provide new information about the relation of bone blood flow to ionic homeostasis. 4) Hypothermia and bone blood flow. We plan to document the effect of hypothermia on bone blood flow, and further, to determine the effect of depressed bone blood flow on the ability of the animal to alter its serum ion levels after hormonal and ionic challenges. This study is designed to improve our understanding of the role of bone blood flow in ionic homeostatis mechanisms.